Crop Yield and Water Quality Benefits of Drainage Water Recycling Chris Hay ISA Conservation Design Specialist chay@iasoybeans.com
D
rainage water recycling is a practice that combines crop production benefits for the farmer and water quality benefits downstream. A drainage water recycling system captures subsurface (tile) drainage and potentially water from surface runoff or other sources, and stores it in a reservoir for supplemental irrigation. The Research Center for Farming Innovation (RCFI) has been collaborating with researchers from Iowa State University to evaluate this practice in Iowa. Three sites are being monitored for the impacts of drainage water recycling on crop yield and water quality. Each site is uniquely designed. The first site, near Story City was installed in 2015. It captures subsurface drainage from about 20 acres that is supplemented by water pumped from a nearby creek. The reservoir for the second site, near Lake City, was constructed in a waterway
fed by the outflow from a large drainage district main and has an outlet structure for when inflows exceed the reservoir storage capacity. The third site, near Dayton, uses a sump to pump water from an adjacent county drainage main into an excavated reservoir.
Crop yield At the Story City site, 60 acres are irrigated and another 100 acres are not irrigated. However, the acres have the same soil type and management, serving as a good control for comparing the irrigated and rainfed yields. Corn yield data has been available since the system began operation in 2016. Yields were greater in the irrigated portion of the field in every year except for 2018, when there was ample rain and no irrigation was used, and in 2020, when the derecho damaged the center pivot. Yield increases ranged from -7 bushels per acre in 2018, when there was no
Lake City 2022
irrigation, to 119 bushels per acre in 2017. The yield increases are largely explained by differences in precipitation, with 2017 precipitation 32% less than the 30-year average whereas precipitation in 2018 was well above the 30-year average. The overall average corn yield increase from the supplemental irrigation was 35 bushels per acre. In addition to greater overall yields, there was less year-to-year variability in yield in the irrigated portion of the field. Yield monitor data show that yields were more consistent in the irrigated portion within individual years.
Water quality With the two new sites in Lake City and Dayton, there are now four site years of water quality monitoring to evaluate the water quality benefits of drainage water recycling. To understand the water balance of each system, inflows and outflows were measured. Those inflows and outflows and the water stored in the reservoir
Lake City 2023
Inflow
Inflow
Outflow
Outflow
Nitrogen loads of drainage water
Irrigation
Irrigation
recycling systems for four site years.
Seepage
Load reductions f rom the systems
Seepage
63%
Reduction 0
1000
2000
3000
92%
Reduction 4000
0
500
Story City 2022
1000
1500
were calculated as nitrogen inflows into the reservoir minus any outflows f rom the reservoir back to the stream
Dayton 2023
and seepage losses. Nitrogen in the
Inflow
Inflow
Outflow
Outflow
available for plant uptake or would
Irrigation
Irrigation
otherwise be reduced and not return
Seepage
Seepage
Reduction
90% Reduction 0
100
200
300
400
irrigation water was assumed to be
to surface water. Units are in pounds 92% 0
Total Nitrogen (lbs.)
20 | FEBRUARY 2024 | IASOYBEANS.COM
250
500
750
1000
of total nitrogen.
